A retarding-voltage-type energy analyzer combining a plural number of grids in the conventional concentrically spherical shape and a fluorescent screen is widely used for low-energy electron diffraction observation and Auger electron spectroscopy measurement. However, there has been a problem that the signal amplification cannot be performed using a planer microchannel plate because charged particles are projected onto a spherical surface due to usage of grids of concentric sphere. In addition, there has been a problem that the retarding-voltage-type energy analyzer shows a poor signal-to-background ratio due to the high-pass-filter effect resulting in unsuitability for a two-dimensional angle distribution measurement such as photoelectron diffraction. In view of this, a retarding-voltage-type energy analyzer which projects the two-dimensional angle distribution on a plane using electrodes of axially symmetric electrodes was proposed (Refer to Patent literature 1 and 2). However, the acceptance angle of the charged particles generated at the point source was limited to ±10°.
In addition, the fluorescent X-ray becomes an obstacle when a retarding-voltage-type energy analyzer is utilized for a measurement of photoelectron diffraction measurement. There has been a problem that the X-ray cannot be removed at the retarding voltage and the fluorescent X-ray dosage increases as the acceptance angle for charged particles is enlarged, which becomes a background noise.
On the other hand, an electrostatic lens is often used at the incident part of an energy analyzer in an apparatus for electron spectroscopy and this electrostatic lens takes in as much electrons as possible and lets the electrons enter into the analyzer after decelerating the electrons, thus the energy resolution capability can be improved. Not only in the apparatus for electron spectroscopy but also in the surface analysis and further in the fundamental research of solid state physics, a technology that enables measurement over a large solid angle range by making the acceptance angle of charged particles wider is demanded because the measurement sensitivity is determined by the extent of the area of the solid angle wherein the charged particles can be accepted in case of such as electron spectroscopy measurement by electrons emitted from the crystal surface, electron diffraction, and ion desorption angle distribution measurement.
Also, if the acceptance angle of the charged particles is less than ±30°, an atomic arrangement structure analysis such as photoelectron diffraction and photoelectron holography is difficult but the atomic arrangement structure analysis becomes possible if the measurement of the large solid angle with the acceptance angle equal to or larger than ±30° is possible.
In ordinary electrostatic lenses, the acceptance angle is limited to about ±20° due to the difficulty of focusing the beam of a large opening angle on one point due to the spherical aberration, however, the acceptance angle has been improved to about ±30° because it is possible to increase the sensitivity by using a spherical mesh (Refer to Patent literature 3).
Also, a spherical aberration correction electrostatic lens capable of realizing a larger acceptance angle than using a spherical mesh is known by creating an optimum electric field using a plural number of electrodes, applying the negative spherical aberration correction effect of the aspherical mesh (Refer to Patent literature 4).
However, as shown in FIG. 21, in the spherical aberration correction electrostatic lens 100 as disclosed in Patent literature 4, an aspherical mesh 106 being shaped as an optically symmetrical spheroid having a concave shape against a sample surface 110 positioned so that an enlarged virtual image having a negative spherical aberration is to be formed, and a plural number of electrodes (101˜105) consisting of a concentric surface for forming a convergence electric field that generates positive spherical aberration that forms a real image of the enlarged virtual image, are being positioned in the configuration and thus the lens itself becomes large-scaled with the distance from the sample surface 110 to the light exit portion 107 being large (L=about 0.5 mm) and resultantly the ultra-high vacuum electromagnetic field shielding chamber (not shown) for storing the sample surface 110 and the aspherical aberration compensation electrostatic lens 100 entirely became enlarged. In addition, the emitted beam becomes a point light source beam with a narrow solid angle due to the influence of convergence electric field that generates equilateral spherical aberration and the beam is emitted from the beam exiting opening 107 and accordingly, in the case wherein the emitted light source beam is projected on a fluorescent screen for energy analysis, it has been difficult to achieve the compactification of the whole apparatus because it is necessary to make the point charged-particle beam needs to be converged once at the exit slit in the case, for example, wherein the electrons emitted from the exiting opening 107 are analyzed by the retarding voltage or the deflection electric field (not shown) and the angle distribution is projected on a fluorescent screen (Not shown).